This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2001-366704 filed on Nov. 30, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel injection valve in which fuel injection amount is accurately adjusted.
2. Description of the Prior Art
To meet recent demands of higher performance and exhaust emission purification of an internal combustion engine, adjustable assembly of component parts is necessary to secure accurate injection amount of fuel to be sprayed from injection bores. Generally, in the fuel injection valve, in particular, in a fuel injection valve of the internal combustion engine for vehicles, a valve operative together with a movable member is driven to open and close the injection bores by permitting and interrupting current apply to a drive coil. An electric control unit is operative to govern a time period during which the current is supplied to the drive coil for controlling a valve-opening period so that the injection amount of fuel to be sprayed from injection bores to the engine is defined. Accurate fuel injection amount is achieved by absorbing manufacturing deviation or fluctuation of the component parts of the fuel injection valve, that is, the adjustable assembly of the component parts of the fuel injection valve has to be carried out for securing accurate injection amount of fuel to be sprayed from the injection bores.
For example, U.S. Pat. No. 5,996,910 discloses the adjustable assembly of component parts for securing the accurate fuel injection amount. According to U.S. Pat. No. 5,996,910, an attracting member is press fitted to an inner circumference of a pipe until an axial end of the attracting member reaches an axial given position of the pipe where a given lift amount of a nozzle needle is ensured.
In a conventional fuel injection valve disclosed in U.S. Pat. No. 5,996,910, pressing load necessary for press fitting the attracting member to the inner circumference of the pipe is variable depending on shape or geometry variation of the inner circumference of the pipe. For example, when component parts are connected to an outer circumference of the pipe by press fitting or welding, the inner circumference of the pipe is prone to be partially and unstably deformed by compression force due to the press fitting or thermal stress due to the welding, even if the respective component parts have accurate dimension before they are connected to the pipe by press fitting or by welding. Accordingly, when the attracting member is press fitted to the inner circumference of the pipe, a relative axial position between the attracting member and the pipe is not precisely predictable since a degree of the partial deformation of the inner circumference of the pipe is variable and the pressing load applied to the attracting member for press fitting is not stable.
To make the shape of the inner circumference of the pipe uniform, it is contemplated to finish the inner circumference of the pipe through a grinding or reaming process. However, this process needs more fabrication time and manufacturing cost.
An object of the present invention is to provide a fuel injection valve in which a valve lift amount is precisely adjusted to define an accurate fuel injection amount by press fitting an attracting member to an inner circumference of an inner pipe member, even if shape of a part of the inner circumference of the inner pipe member is not uniform due to an outer frame member connected to an outer circumference thereof.
To achieve the above object, in a fuel injection valve in which a valve member moves axially and reciprocatingly, an inner pipe member has first and second zones through which magnetic flux easily pass, respectively and a third zone through which magnetic flux hardly passes and which is positioned axially between the first and second zones. A drive coil is arranged around an outer circumference of the inner pipe member. An outer frame member is connected, for example, by press fitting or welding, to the outer circumference of the inner pipe member at first and second limited regions falling within the first and second zones, respectively, in such a manner that the drive coil is sandwiched radially between the outer frame member and the inner pipe member. An attracting member is press fitted to the inner circumference of the metal inner pipe member so that an axial end of the attracting member is positioned axially within the third zone and the other axial end thereof is positioned axially within the first zone. A movable member, whose axial end is connected to the valve member, is accommodated to move axially and reciprocatingly within an inner circumference of the inner pipe member. The axial end of the movable member is positioned axially within the second zone and the other axial end thereof is positioned axially within the third zone so that the movable member is axially away by a given distance from the axial end of the attracting member, when the drive coil is not energized, and attracted toward the axial end of the attracting member by magnetic flux passing through the outer frame member, the first zone, the movable member and the second zone, when the drive coil is energized.
With the fuel injection valve mentioned above, an outer circumference of the attracting member and/or the inner circumference of the inner pipe member is provided with a relief space which prevents the outer circumference of the attracting member from coming in contact with the inner circumference of the inner pipe member at least at a position just radially inside and axially corresponding to the first limited region.
Even if the inner circumference of the inner pipe member at the position axially corresponding to the first limited region is variably deformed by pressing force or thermal stress when the outer frame member is press fitted or welded to the outer circumference of the inner pipe member, the relief space prevents the outer circumference of the attracting member from coming in contact with the inner circumference of the inner pipe member at a position just radially inside and axially corresponding to the first limited region, when the pressing load is applied to the attracting member for press fitting the attracting member to the inner pipe member for a valve lift adjustment. Accordingly, an axial position of the attracting member relative to the inner pipe member is precisely adjusted by press fitting the attracting member to the inner pipe member so that a valve lift amount is accurately defined, since the relief space effectively absorbs the possible deformation of the inner circumference of the inner pipe member at the position axially corresponding to the first limited region.
It is preferable that the outer circumference of the attracting member is in contact with the inner circumference of the inner pipe member only at a position axially between the first and second limited regions. In more details, diameter of the inner circumference of the inner pipe member with which the outer circumference of the attracting member is not in contact in the first zone is larger than that of the inner circumference of the inner pipe with which the outer circumference of the attracting member is in contact. In this case, the attracting member is easily inserted and press fitted to the inner pipe member from an axial end of the first zone on a side remote from the third zone since it is not necessary to substantially press the attracting member to the inner pipe member until the axial end of the attracting member axially exceeds the first limited region in the first zone.
In addition, preferably, a diameter of the outer circumference of the attracting member in contact with the inner circumference of the inner pipe member is larger than that of the outer circumference of the attracting member not in contact with the inner circumference of the inner pipe member at least at a portion axially corresponding to the first limited region. In this case, not only the attracting member is more easily press fitted to the inner pipe member, but also the possible contact between the outer circumference of the attracting member and the inner circumference of the inner pipe member at the position axially corresponding to the first limited region can be more definitely avoided.
Further, instead of the relief space provided on a side of the inner circumference of the inner pipe member, the attracting member may be provided on and along the outer circumference thereof with an annular recess such as a groove, as a relief space, which prevents the outer circumference of the attracting member from coming in contact with the inner circumference of the inner pipe member at the position axially corresponding to the first limited region.
Furthermore, it is preferable that the fuel injection valve has an adjusting pipe press fitted to an inner circumference of the attracting member and a spring disposed at least partly within the inner circumference of the attracting member and sandwiched axially between the movable member and the adjusting pipe for urging the movable member axially in a direction away from the attracting member.
With this valve, if the relief space provided on the outer circumference of the attracting member is positioned axially in a middle of the adjusting pipe press fitted to the inner circumference of the attracting member and diameters of the outer circumference of the attracting member axially outside the relief space are equal to each other, the relief space not only prevents the outer circumference of the attracting member from coming in contact with the inner circumference of the inner pipe member at a position axially corresponding to the first limited region but also serves to keep an adequate stiffness of the attracting member to an extent that the adjusting member is precisely press fitted to the inner circumference of the attracting member.